[Alneyan]

Are you playing Proportions #3, and not #2? If so, you will find that there is only one, uber facility in your homeworld, and everything else is mundane. That one facility is *very* important, so be sure to protect it! Other than that, you can customise your homeworld: do you wish more research? Build more research centres at home then, and scrap those mining facilities, and watch your research soar.

Your other colonies are going to want some cultural facilities too, but the Homeworld ones take *thousands* of turns to be completed on most planets, so let's forget about them. In #3, Cultural facilities are a lot more attractive because of their planet-wide bonuses: for example, a middle-level Metropolis gives X5 to mineral production, among others.

Upgrading your cultural facilities is usually the best option, as it is cheaper, faster, and brings you some benefit along the way. Minor Cities are the first cultural facility that allow to upgrade all the way up to Arcology, so you may want to build these if you would like to improve it further afterwards. Colonial communities are very cheap and give a lot of bang for the buck, but they are a dead-end; Spaceport Cities are nice, but are also a dead-end.